The so-called "plate design" is supposed to replace the "Food pyramid", which was allegedly supposed to tell us that we should eat many carbohydrates and few fats, on balance.
But is this sort of thing valid, or was it simply a matter of what the Department of Agriculture wanted people to believe?
Let's remember that the cost of food as a percentage of income has been on a relentless slide for the entirety of the United States' existence. And no small part of that change has come from the belief that a calorie is a calorie.
In terms of energy content for the body, this is true. But in terms of what your body does, it is absolutely not.
Simple carbohydrates, such as sugars and starches easily convertible to sugars in the body, provide quick energy. But the body's actual consumption of energy is more-or-less a constant. When you're exercising the instantaneous demand rate is higher, when sitting quietly lower.
Now here's the problem: If the energy released into your bloodstream in the form of available energy exceeds the burn-up rate at that moment, the body responds by converting that energy resource to fat.
These spikes in the balance of available energy to consumed energy also cause a massive insulin response.
There is plenty of reason to believe that these "quick spikes" in insulin response contribute to the formation of Type II diabetes - insulin resistance. Over the years repeated insults of this sort would be reasonably expected to dull the response mechanism, and thus lead to higher blood sugar levels. That's bad.
But has anyone in the mainstream dietary press talked about this? Oh hell no. We can't possibly anger The Agriculture Department, especially when a huge percentage of that corn is turned into the "robofood" called "High Fructose Corn Syrup."
That's an engineered calorie source that is designed to mimic sugar in "sweetness." It's used because it's cheaper than cane sugar. It contains a mixture of fructose and glucose, and importantly while the glucose in the mixture produces an immediate insulin response by the pancreas the fructose does not. Why is this important? Primarily because the "satisfied" feeling (that deters further eating) is stimulated via two pathways: fat in the gut and high insulin levels in the blood. Without that response you do not feel "full" and thus although you've taken in calories in the form of fructose there's no bodily response to that consumption that tells you to stop eating.
Worse, this stuff is in damn near everything nowdays.
Fifty years ago, it wasn't in anything; it appeared in the United States, more or less, in 1975.